Can high-precision optics be 3D printed?

Not yet - optical components are some of the highest precision products manufactured today with surface accuracies of tens of nanometers, surface roughness values in the tens of angstroms range, and very high levels of internal (index of refraction) homogeneity being common. Current 3D printing and additive manufacturing techniques yield parts with specification tolerances that are many orders of magnitude larger than what traditional manufacturing methods can deliver. Other than select illumination or beam shaping applications, 3D printing is not going to produce precision optics within the near future.